Author
Topic: Leaky Carb (Read 1781 times)

I am having a problem with my stock 28MM Micarb carburetor on my Bullet 500. My float bowl continues to overflow and fuel spills out of the overflow tube attached to the bottom of the float bowl.

Here are the steps I have taken to correct this:

- Thoroughly cleaned the carb with carb cleaner and compressed air several times- Adjusted the float level numerous times, even once to an extreme to see if I could get the carb from over flowing-replaced carb float, hinge pin, the needle valve and seat the control the fuel flow, and the carb gasket

None of the above changes have made a difference

I have rigged up a mock fuel system to work on the carb off the bike

I took a Nalgeene hydration pack bladder and hung in above my workbench. The tube the goes out of this is just big enough to slide the stock fuel line into. I did this then took the float bowl off the carb and set the carb on top of a small whiskey glass. This way I can watch fuel (water) come into the carb, the float rise and wait for the (fuel) water to stop. Here is what I am observing. Water will come in and the float will start to rise to a certain point then the water seems to stop rising, but if you watch closely and give it 30 seconds the water rises to the top of the glass.

Does anyone have a suggestion on what is causing this? It almost seems as if the fuel (or water in the test) that elevates the float is not applying enough pressure to close the needle valve.

I have had the carb on and off probably 20 times over the past two weekends with no success at all.

I am open to suggestions of if someone has a 28MM Micarb they want to sell me at a good price I would be willing to take it off their hands.

i just thought of something. this questions is for anyone that is familiar with the stock carb. I think i may have the needle assembly inverted. I am looking at a parts catalog and this may be my problem. When you assemble the needle valve that controls the fuel flow should the pointy end of the small, blunt end with a spring be touching the float tang?

I am also unsure on how to measure float bowl height. I know that the suggested height is 25-28MM but do you measure it with the float bowl off and the carb situated like it is when installed on the bike or do you turn it upside down and measure? I am assuming the measurement should be done from the gasket area with the gasket installed. Clarification on this would be appreciated.

On any float needle and seat I have ever seen, the pointy end of the needle goes into the seat. The blunt end of the needle goes against the tab on the float.

Imeassure float height by taking the bottom off the float chamber and turning the carb upside down. With nothing but gravity pulling the float down onto the needle and seat, measure the height from the surface where the float bottom matches up to, to the top of the round part of the float.

Now, that's how I used to do it. I'm sure others will have suggestions as well.

You got good advice below. The pointy end goes up into the seat. Measure the float level just like was suggested below and be aware that these can be a wear item. Sometimes these needles and seats can be a mystery of the universe. One of the reasons for a fuel cut-off valve is becuase these things can leak for no apparant reason while the bike is in your garage. This only happens at night when no one is around and otherwise they can work fine. This has happened to me many times.

They are speak'n the truth. Do you use the shutoff?? I never did till mine started that mystery drip last year. Now I do and it's not a problem. You might want to get in the habit of flipping it as you pull in the drive to get the level down just a little in the bowl. - Mike

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'My dear you are ugly, but tomorrow I shall be sober and you will still be ugly' - Winston Churchill

Thanks guys. I do use the shut off religiously. This problem was happening pretty much as soon as you turned the fuel flow on. In my troubleshooting I replaced the needle and seat as well as the float so hopefully they are good for a long while. I had the needle valve that controls the flow of fuel in backwards... such a dumb but easy mistake.

Best way to learn... have you left the kill switch off and spent hours troubleshooting yet??

hahah... yeah. after i put my primary back together i couldn’t get the bike to start... i spent about 2 hours trying to figure out what was wrong. I was looking at a wiring diagram and caw the broken circuit for the kill switch. I was relieved it was something so easy and taken care of but felt like a complete fool.

Best way to learn... have you left the kill switch off and spent hours troubleshooting yet??

hahah... yeah. after i put my primary back together i couldn’t get the bike to start... i spent about 2 hours trying to figure out what was wrong. I was looking at a wiring diagram and caw the broken circuit for the kill switch. I was relieved it was something so easy and taken care of but felt like a complete fool.

Yep. Several years ago when I trailored my new 2000 Ural Deco home half way across the country in the snow: unloaded it the same evening and it would not start. Drained the battery and everything before I realized the kill switch was engaged...DOH!

It was big of you to admit your mistake. I was amused at all of the hugely technical "well in deep theory it might be because of some mysterious force of nature" comments I saw elsewhere. If there is one thing I have learned over the years, is that it is ALWAYS the simple stuff, like the needle being in backwards, kill switch off etc and almost NEVER the things that keep you up at night. When I was a high school shop teacher the kids thought I was some sort of mystical genius because 99% of the time I could diagnose the issues with their cars from an arms length away. I am not smart at all, but I have learned to look at the most basic things first.

Reminds me of the time I was living with a buddy several years ago and our shower stopped draining. I worked on it for like four hours, plunging the hell out of it (got blisters on my hands), pouring in like a gallon of Draino (the fumes!), and finally calling a plumber much to the landlord's expense (and annoyance). Before even saying "hello" the plumber flipped the drain stopper lever and the water-Draino solution disappeared like normal.

All was not lost, though, since we asked him to repair the constantly-running toilet that we'd neglected for months.